Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2993268AbbHHWMt (ORCPT ); Sat, 8 Aug 2015 18:12:49 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36220 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2992743AbbHHWMn (ORCPT ); Sat, 8 Aug 2015 18:12:43 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "J. Bruce Fields" , Al Viro Subject: [PATCH 4.1 021/123] freeing unlinked file indefinitely delayed Date: Sat, 8 Aug 2015 15:08:19 -0700 Message-Id: <20150808220718.610827751@linuxfoundation.org> X-Mailer: git-send-email 2.5.0 In-Reply-To: <20150808220717.771230091@linuxfoundation.org> References: <20150808220717.771230091@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4027 Lines: 113 4.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit 75a6f82a0d10ef8f13cd8fe7212911a0252ab99e upstream. Normally opening a file, unlinking it and then closing will have the inode freed upon close() (provided that it's not otherwise busy and has no remaining links, of course). However, there's one case where that does *not* happen. Namely, if you open it by fhandle with cold dcache, then unlink() and close(). In normal case you get d_delete() in unlink(2) notice that dentry is busy and unhash it; on the final dput() it will be forcibly evicted from dcache, triggering iput() and inode removal. In this case, though, we end up with *two* dentries - disconnected (created by open-by-fhandle) and regular one (used by unlink()). The latter will have its reference to inode dropped just fine, but the former will not - it's considered hashed (it is on the ->s_anon list), so it will stay around until the memory pressure will finally do it in. As the result, we have the final iput() delayed indefinitely. It's trivial to reproduce - void flush_dcache(void) { system("mount -o remount,rw /"); } static char buf[20 * 1024 * 1024]; main() { int fd; union { struct file_handle f; char buf[MAX_HANDLE_SZ]; } x; int m; x.f.handle_bytes = sizeof(x); chdir("/root"); mkdir("foo", 0700); fd = open("foo/bar", O_CREAT | O_RDWR, 0600); close(fd); name_to_handle_at(AT_FDCWD, "foo/bar", &x.f, &m, 0); flush_dcache(); fd = open_by_handle_at(AT_FDCWD, &x.f, O_RDWR); unlink("foo/bar"); write(fd, buf, sizeof(buf)); system("df ."); /* 20Mb eaten */ close(fd); system("df ."); /* should've freed those 20Mb */ flush_dcache(); system("df ."); /* should be the same as #2 */ } will spit out something like Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 322023 303843 1131 100% / Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 322023 303843 1131 100% / Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 322023 283282 21692 93% / - inode gets freed only when dentry is finally evicted (here we trigger than by remount; normally it would've happened in response to memory pressure hell knows when). Acked-by: J. Bruce Fields Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/dcache.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -642,7 +642,7 @@ static inline bool fast_dput(struct dent /* * If we have a d_op->d_delete() operation, we sould not - * let the dentry count go to zero, so use "put__or_lock". + * let the dentry count go to zero, so use "put_or_lock". */ if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) return lockref_put_or_lock(&dentry->d_lockref); @@ -697,7 +697,7 @@ static inline bool fast_dput(struct dent */ smp_rmb(); d_flags = ACCESS_ONCE(dentry->d_flags); - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST; + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; /* Nothing to do? Dropping the reference was all we needed? */ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) @@ -776,6 +776,9 @@ repeat: if (unlikely(d_unhashed(dentry))) goto kill_it; + if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED)) + goto kill_it; + if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) { if (dentry->d_op->d_delete(dentry)) goto kill_it; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/